Fix manual depth test hole cutting

modules/base/shaders/model_fs.glsl

@@ -25,7 +25,6 @@
 #include "fragment.glsl"
 
 in vec2 vs_st;
-in vec2 vs_viewportPixelCoord;
 in vec3 vs_normalViewSpace;
 in vec4 vs_positionCameraSpace;
 in float vs_screenSpaceDepth;
@@ -51,6 +50,9 @@ uniform float lightIntensities[8];
 uniform bool performManualDepthTest = false;
 uniform sampler2D gBufferDepthTexture;
 
+uniform vec4 viewport;
+uniform vec2 resolution;
+
 Fragment getFragment() {
   Fragment frag;
   frag.depth = vs_screenSpaceDepth;
@@ -60,9 +62,27 @@ Fragment getFragment() {
   frag.color.a = 1.0;
 
   if (performManualDepthTest) {
+    // gl_FragCoord.x goes from 0 to resolution.x and gl_FragCoord.y goes from 0 to
+    // resolution.y, need to normalize it
+    vec2 texCoord = gl_FragCoord.xy;
+    texCoord.x = texCoord.x / resolution.x;
+    texCoord.y = texCoord.y / resolution.y;
+
+    // Modify the texCoord based on the Viewport and Resolution. This modification is
+    // necessary in case of side-by-side stereo as we only want to access the part of the
+    // feeding texture that we are currently responsible for.  Otherwise we would map the
+    // entire feeding texture into our half of the result texture, leading to a doubling
+    // of the "missing" half. If you don't believe me, load a configuration file with the
+    // side_by_side stereo mode enabled, disable FXAA, and remove this modification.
+    // The same calculation is done in the FXAA shader, the HDR resolving and the
+    // atmosphere shader
+    vec2 st = texCoord;
+    st.x = st.x / (resolution.x / viewport[2]) + (viewport[0] / resolution.x);
+    st.y = st.y / (resolution.y / viewport[3]) + (viewport[1] / resolution.y);
+
     // Manual depth test
     float gBufferDepth =
-      denormalizeFloat(texture(gBufferDepthTexture, vs_viewportPixelCoord).x);
+      denormalizeFloat(texture(gBufferDepthTexture, st).x);
     if (vs_screenSpaceDepth > gBufferDepth) {
       frag.color = vec4(0.0);
       frag.depth = gBufferDepth;